Process for removing mercaptan sulfur



United States Patent C PROCESS FOR REMOVING MERCAJTAN ,SULFUR WITH AN ORGANIC PHOSPHI'IE William L. Fierce, Crystal Lake, and Walter]. Sandner,

Carpentersvi'lle, 111., .assignous :to The Pure Dil Company, Chicago, 111., a ecorpnration'of Ohio "N Drawing. Application November '18, I957 Seria'l'No. 696,971

.14 Claims. ((31. cos-237;

This invention relates to improving'the odor and minimizing the corrosiveness of petroleumfract'ions. It is more specifically concerned with the substantially complete elimination of mercaptan-sulfur from mercaptancontaining petroleum fractions.

According to this invention,-the substantially complete reduction "of mercaptan-sulfur in petroleum distillates can be effected by intimately contacting the mer- 2,899,386 Pal-tented Aug. 11, 1959 'ice @2 duction of :disulfides in the finished gasolines, this'type of process is limited with regard to the final merca ptan-suh for content which can he produced in the finished gasoor other petroleum product which is treated. Al-

though total sulfur reduction can be produced in various product. Another object :of this invention is to provide captan-conta ining petroleum distillate, which is substantially free from dissolved or absorbed oxygen, with an organic phosphite having the general formula,

'RI! -o j where R, R and'R are selected fromthe group consisting of alkyl and cycloalkyl constituents, which provide organic phosphites soluble inflight petroleum distillates, in an amount sulficient to effect the removal of said mercaptans, but not less than about 20 mols weight of Organic phosphite per mol of mercaptan sulfur in the petroleum distillate being treated, at a temperature within the range of about 50 to 200'F. I p

The presence of mercaptans in'lowand middle-boiling petroleum hydrocarbon products, such as gasolines, naphthas, kerosines and fuel oils, has a number of disadvantages. In gasolines and naphthas, the presence of 0.005 weight percent of mercaptan sulfur, and even, as little as 0.002 weight percent, produces undesirable odors in the petroleum products. 'In excess "of about 0.005 weight percent of 'mercaptansulfur imparts undesirable corrosivenes to gasoh'nes. Aryl thiols such as this: phenols and its homologs present in gasolines, kerosines, fuel oils and the like have an adverse eifect on the storage stability of these petroleum products. In addition, mercaptans have an antagonistic'influence on the lead susceptibility and octane rating of gasolines. It is therefore evident that these and other disadvantages make it important that mercaptans 'be eliminated from petroleum products of this-nature,

Treating processes which are employed in the refining of mercaptan-containing gasolines in general fall into two broad classes:

(1) Those which chemically convert the mercaptans to other compounds such as disulfides, e.g., doctor-treating process, copper chloride, hypochlorite, lead sulfide, and other oxidative processes; and

(2) Those which extract mercaptans, e.g., caustic .a treating process which minimizes the mercaptan-sulfur content of petroleum distillates without increasing the disulfide-sulfur content of the treated gasoline. It is a further object of this invention to provide a treating process for the substantially complete removal of mercaptans from distillat'es by employing an economical process utilizing conventional petroleum refinery equipment. These and other objects will become more apparent from the following detailed description of this scrubbing, Shell Solutizer process, [Pure Oil 'Mercapsol process, and Atlantic U nisol process,

Unfortunately, however, these processes are not free from disadvantages which arise from their use. For example, in the former type of process wherein the mercaptans are chemically converted to disulfides 'anunwithout solubility promoters, does not result in the proinvention.

According to this invention, the substantially complete reduction in the mercaptan-sulfur content of a lowor middle-boiling petroleum fraction can be economically carried out without increasing the disullidc-sulfur content of the treated petroleum feed-stock by intimately contacting a mercaptan-containing petroleum traction, such as naphtha, gasoline, kerosine, or .fuel oil which is substantially free from dissolved or adsorbed oxygen, with an organic phosphite having thegen'eral formula:

where R, R and R'" are aliphatic or alicyclic substituents having 1 to 15 carbonatoms per molecule which provide an organic phosphite soluble in a naphtha or petroleum fraction. Sufiicient amounts of the selected organic phosphites to sweeten the fraction, in excess of .about '20 mols of phosphite per mol of mercaptan sulfur contained in the petroleum fraction being treated, are incorporated in the mercaptan-containing petroleum feed-stock, and the mixture is maintained in intimate contact for a time suificient to efiect the substantially complete reduction of the mercaptan-sulfur content of the petroleum fraction treated in accordance with this invention. Because the organic phosphites employed are completely soluble in the petroleum distillate being treated, it is only necessary to employ mechanical mixing during the introduction of the phospite treating agent. When the phosphite treating agent is completely in solution, it is only necessary to retain the admixture in a quiescent state to eliect the reduction of the mercaptansulfur content of the gasoline. The processing can be carried out at relatively low temperature, generally at temperatures Within the range of about 50 F. up to about the boiling point of the fraction being treated.

The naphtha or other petroleum fraction treated must be substantially free from dissolved oxygen in order to successfully carry out the process of this invention. Generally petroleum products, which are treated in accordance with this invention, immediately after separation from the crude petroleum oil are substantially oxygen free. Products, however, which have been in storage and exposed to air prior to processing will contain amounts of free oxygen absorbed therein which will deleteriously affect the efiiciency of the process of this invention. Ac cordingly, stored products must be purged with an inert gas such as nitrogen, flue gas, dry normally gaseous hydrocarbons, or other similar substances, in order to deaerate or deoxygenate the petroleum-derived feed stock prior to treating to effect the reduction of mercaptan sulfur content. Other deaeration techniques can also be used such as contacting the oxygen-containing feed stock with an oxygen susceptible reagent such as metallic copper. Certain petroleum products such as straight-run naphthas, and cracked gasolines are susceptible to peroxidation. It is preferred that the straight-run products, which are subsequently to be treated in accordance with this invention, be purged of any free oxygen prior to being sent to storage and that the purged petroleum product be stored in facilities which provide an inert gas blanket in V In addition other qualitative techniques for determining H I the presence of dissolved or absorbed oxygen vn'll be apparent to those skilled in the art.

To facilitate the handling of the treating agent, it is preferred that a liquid organic phosphite soluble in naphtha or petroleum fraction be employed. In the alternative, however, soluble solid organic phosphites are also effective and can be employed if desired. In this event, it may be preferred to utilize a petroleum fraction concentrate of the selected organic phosphite. Examples of organic phosphites which are effective for the removal of mercaptans from petroleum fractions include but are not limited to trimethyl phosphite, triethyl phosphite, tri-npropyl phosphite, tri-Z-propyl phosphite, tributyl phosphite, triisobutyl phosphite, triamyl phosphite, trihexyl phosphite, tri-Z-ethylhexyl phosphite, triisooctyl phosphite, tricyclohexyl phosphite and others. It is to be noted that in carrying out the treating process of this invention triaryl phosphites and other related compounds, such as fining of a number of light petroleum fractions, it is preferably employed in the manufacture of specialty naphthas which must conform with rigorous specifications regarding odor and mercaptan-sulfur content. In the event that gasolines or petroleum fractions intended for use as gasoline blending components are to be treated, the reaction products formed during the course of the treating process can remain in the treated gasoline because the products so formed are soluble in gasoline, are noncorrosive, and act as pre-ignition suppressers on the combustion of gasoline during use. Because the products contained in the petroleum fraction treated in accordance with this technique are substantially innocuous, it may be satisfactory, even when treating specialty naphthas to substantially reduce the mercaptan-sulfur content, to permit these products to remain in the naphtha. In the event, however, that it is desired to separate the treated naphtha from the products resulting from the treating step, simple distillation can be utilized by employing an organic phosphite so selected that it and the reaction product formed by it during the course of the treating step boil either below or preferably above the boiling range of the finished naphtha. The selected organic phosphite is added to the mercaptan-containing naphtha and after the treating step is completed, the resulting mixture is distilled so that the phosphorus-containing reaction products are separated either by being distilled first from the naphtha, or by being left in the bottoms from the distillation of the mixture.

The amount of organic phosphite employed in reducing the mercaptan-sulfur content of the petroleum fraction being treated will, in general, depend upon the amount the alkyl and aryl phosphates, are ineffective for reducing sufiicient amount of the selected organic phosphite into a storage facility which is preferably one in which the mercaptan-containing petroleum fraction is contained. A mixing device installed in the storage facility is employed to effect the intimate admixing of the treating agent and the petroleum fraction. agent has been dissolved in the petroleum fraction to be treated, the mixing can be stopped and the solution allowed to remain at rest until the desired reduction in After the treating mercaptan sulfur content of the treated petroleum fraction is effected. If, on the other hand, it is preferred that the treating step be carried out at an elevated temperature in order to facilitate the treatment, conventional refining equipment suitable for contacting the treated petroleum fraction at an elevated temperature, in which an intimate admixing of the treating agent and the petroleum feed stock can be carried out, is used.

Although the instant process has application in the reof mercaptan which is in the petroleum feed-stock. It has been found that large molar excesses of the selected organic phosphite are required in order to elfect a substantial reduction in the mercaptan-sulfur content of the treated feed-stock. The amount of mercaptan present in various hydrocarbon compositions often is small, frequently less than 0.10% by weight. Accordingly, it would be expected that only small amounts of the organic phosphite would be necessary. It has been found, however, that amounts substantially in excess of equimolar amountsof the treating agent and mercaptan must be employed. In general, an excess of about 20-40 times the number of mols of mercaptan sulfur present in the feed stock being treated are required. The exact amount required can be determined by experimentation employing small samples of the feed-stock to be treated. Accordingly, a ratio of about 20-40 mols of treating agent per mol of mercaptan-sulfur in the petroleum fraction being treated is ordinarily used, but in some instances amounts in excess of this range of treating agent may be required.

Various qualitative and quantitative methods are available for determining the presence and/or concentration of mercaptans in the petroleum fraction to be treated. Mercaptaus can be detected by the well-known doctor test, or by contacting the selected sample with a solutron of sodium nitroprusside and a sodium hydroxide solutlon. The development of a purple color indicates the presence of mercaptan. The usual quantitative methods consist in titrating mercaptans with silver nitrate or ammoniacal copper sulfate solutions. A number of these techniques are outlined in a discussion of analytical methods and details by Kalichevsky in Sweetening and Desulfurization of Light Petroleum Products," Petroleum Refiner, 29 (12), pp. 97 et seq.

In testing the treated product to determine the effectrveness of the treat, a sample of the finished product is distilled at atmospheric pressure and the distillate recovered in 10% cuts. This technique is necessary because the desired phosphite treating agent interferes with the doctor test.

V Y Compositions especially adaptable to treatment by the process of this invention are petroleum fractions boil- .ing upto about 750 F. at atmospheric pressure. These, include light distillates, such as industrial petroleum naphthas and solvents; gasoline-type motor fuels and motor fuel blending components; kerosines, and the middle 6 from the scope of the instant invention. Accordingly, the instant invention, which is concerned with the substantial reduction the mercaptan-sulfur content ofa petroleum fraction by contacting the fraction with an distillates, such as diesel fuels, heater and furnace oils; 5 organic phosphite in amounts and for a time sufiicient etc. to produce a treated fraction substantially free from The following examples demonstrate the effectiveness mercaptan sulfur, is limited only in the manner specificalof this invention. 1y set forth in the appended claims.

A plurality of samples of a low-sulfur naphtha derived What is claimed is: fromaMid-Continent crude, havingaASTM boilingrange A .p for substantially reducing the nof 111 F. I.B.P. to 414 F. E.P. containing 0.022 weight tan-sulfur content and odor of a mercaptan-containing percent mercaptanesulfur, and having a poor odor, were petroleum fraction which is substantially free from disprocessed employing a variety of treating agents as well solved oxygen, which comprises intimately contacting as diiferent manipulative techniques. The samples after said fract1on with an organic phosphite from the group treatment were analyzed for mercaptan-sulfur by distillconsisting of alkyl and cycloalkyl phosphites which is ing the samples and subjecting the distillate to the docsoluble in said hydrocarbon feed employing .suificient tor test. In addition, the odors were evaluated by an amounts not less than about mols of phosphite per organoleptic panel of three :men for the presence of odor. mol of mercaptan-sulfur and for .a time sufficient to The samples tested and the results obtained are tabulated reduce the mercaptan-sulfur content of said fraction to in Table I. 20 produce a doctor sweet product.

Table l Moles Vol. Per- Days Wt. Per- Phosphorus Compound Phosphorus cent Phos- Stored Other Odor cent Doctor Sample Used Compound phorus at Room Treatment Evaluation Mercaptan Test No. Per Mole Compound Tempera- (SeeNotes) urs Mercaptan inNaphtha ture l norm 0.0 0.0 9 0.022 S0111. 2 Tributyl Phosphlte 6.7 1.0 '4 8 0.016 I Do. a on 33.5 5.0 4 6 0.002 Sweet. 4 33. 5 5.0 4 6 0. 002 Do. 5 33.5 6.0 .1 6 a 33. 5 5. 0 0 8 0.017 7 33.5 5.0 0 Sour. a 33.5 5.0 0 Do. 0 07.0 10.0 0 Do. lo 33. 5 5. 0 v 1' Sweet.

26.8 4.0 l 2 Sour. 20.1 3.0 8 Sweet 13. 4 2. 0 8 Sour. 33.5 5.0 '7 Sweet 33.5 5.0 I 7 Sour. 31. S 3. 0 3 Sweet 21.2 2.0 3 Sour. 33. 3 5.0 .14 0.013 130. Phospha 29. 7 5. 0 14 0. 011 Do. Triphenyl Phosphite 33. 7 6.0 14 '0. 015 Do.

a The solution of naphtha and phosphite was refluxed for five hours and then allowed to stand at room temperature for 4 days. b The solution-of naphtha and phosphite wasretluxed for 22 hours and then allowed to stand at room temperature for one day. a The solution of naphtha and phosphite was distilled immediately after mixing d The solution of naphtha and phosphite was refluxed for 6 hours and then distilled.

Q The naphtha was purged thoroughly with nitrogen to remove air before treatment and stored under nitrogen.

I The naphtha was purged with oxygen before treatment and stored under oxygen.

From the data tabulated in Table I the unusual or unexpected results produced by the process of this invention are readily seen, whereby doctor-sweet products are produced employing several non-aromatic phosphite treating agents. It is to be noted that while one would expect equimolar amounts of phosphite and mercaptan sul fur to effectively function to convert the mercaptan sulfur to an innocuous phosphorusand sulfur-containing compound, these amounts are not operative. In contradistinction, it is necessary to have a substantial excess of organic phosphite in order to reduce the mercaptansulfur content of the petroleum feed stock to a substantial degree. In addition, it is to be noted that the process of this invention will not operatively function employing triaryl phosphites as is demonstrated by the use of triphenyl phosphite. In addition, analogous phosphorus compounds, such as the organic esters of phosphoric acid, viz., phosphates, also failed as agents for substantially reducing the mercaptan-sulfur content of the petroleum fraction treated. It is to be noted that in these instances neither the aliphatic, alicyclic nor aryl phosphates had utility for reducing the mercaptan content of the feedstock. The feature of employing an oxygen-free feed stock is also illustrated by the tabulated data.

It will be evident to one skilled in the art to which this invention pertains that modifications and variations can be made in the manipulative treating process de scribed in the illustrative embodiment without departing 2. A process for substantially reducing the mercappetroleum fraction which is substantially free from. dissolved oxygen, 'which comprises intimately contacting said fraction with-an alkyl phosphite which is soluble in said petroleum fraction, employing sufficient amounts not less than about 20 mols of phosphite per mol of mercaptan sulfur and for a time sufiicient to produce a doctor sweet product.

3. A process for substantially reducing the mercaptan-sulfur content and odor of a mercaptan-containing petroleum fraction which is substantially free from dissolved oxygen, which comprises intimately contacting said fraction with an alkyl phosphite which is soluble in said petroleum fraction, employing sufiicient amounts not less than about 20 to 40 mols of phosphite per mol of mercaptan sulfur and for a time sufficient to produce a doctor sweet product, said contacting being carried out at a temperature within the range of about 50 F. to the initial boiling point of the petroleum fraction.

4. A process in accordance with claim 3 in which said alkyl phosphite is tributyl phosphite.

5. A process for substantially reducing the mercaptan sulfur content and odor of a mercaptan-containing petroleum naphtha boiling within the range of about 400 P. which is substantially free from dissolved oxygen, which comprises intimately contacting said naphtha with tri-normal-butyl phosphite employing sufiicient amounts within the range of about 20 to 40 mols of phosphite per mol of mercaptan sulfur and for a time suflicient to reduce the mercaptan-sulfur content of said fraction to produce a doctor sweet product, said contacting being carried out at a temperature Within the range of about 50 F. to the initial boiling point of the naphtha.

6. A process for substantially reducing the mercaptan sulfur content and odor of a mercaptan-containing petroleum fraction which comprises deoxygenating said fraction to effect the substantially complete removal of any free oxygen contained therein, and thereafter contacting said fraction with an organic phosphite from the group consisting of alkyl and cycloalkyl phosphites which is soluble in said feed stocks, employing sufficient amounts not less than about 20 mols of phosphite per mol of mercaptan sulfur and for a time sufficient to reduce the mercaptan sulfur content of said fraction to produce a doctor sweet product.

7. A process for substantially reducing the mercaptan sulfur content and odor of a mercaptan containing petroleum fraction which comprises purging said petroleum fraction with an inert gas to effect the substantially complete removal of any dissolved oxygen contained therein and thereafter intimately contacting said deoxygenated fraction with an organic phosphite from the group consisting of alkyl and cycloalkyl phosphites which is soluble in said hydrocarbon fraction, employing suflicient amounts not less than about 20 mols of phosphite per mol of mercaptan sulfur and for a time sulficient to reduce the mercaptan sulfur contentof said fraction to produce a doctor sweet product.

8. A process for substantially reducing the mercaptan sulfur content and odor of a mercaptan containing petroleum fraction which comprises purging said pe troleum fraction with an inert gas to effect the substantially complete removal of any dissolved oxygen contained therein and thereafter intimately contacting said fraction with an alkyl phosphite which is soluble in said petroleum fraction, employing sufficient amounts not less than about 20 mols of phosphite per mol of mercaptan sulfur and for a time sufiicient to produce a doctor sweet fraction with an alkyl phosphite which is soluble in said petroleum fraction, employing sufficient amounts not less than about 20 to 40 mols of phosphite per mol of mercaptan sulfur and for a time suflicient to produce a doctor sweet product.

10 A process for substantially reducing the mercaptan sulfur content andv odor of a mercaptan containing petroleum fraction which comprises purging said petroleum fraction with an inert gas to effect the substantially complete removal of any dissolved oxygen contained therein and thereafter intimately contacting said fraction with an ,alkyl phosphite which is soluble in said petroleum fraction, employing sufficient amounts not less than about 20 to 40 mols of phosphite per mol of mercaptan sulfur and for a time sutficient to produce a doctor sweet product, said contacting being carried out at a temperature within the range of about 50 F. to the initial boiling point of the petroleum fraction.

11. A process in accordance with claim 10 in which said alkyl phosphite isrtributyl phosphite.

12. A process for substantially reducing the mercaptan sulfur content and odor of a mercaptan containing petroleum fraction which comprises purging said petroleum fraction with an inert gas to effect the substantially complete removal of any dissolved oxygen contained therein and thereafter intimately contacting said naphtha with tri-normal-butyl phosphite employing suflicient amounts within the range of about 20 to 40 mols of phosphite per mol of mercaptan sulfur and for a time suflicient to reduce the mercaptan-sulfur content of said fraction to produce a doctor sweet product, said contacting being carried out at a temperature within the range of about 50 F. to the initial boiling point of the naphtha.

13. A process for substantially reducing the mercaptan sulfur content and odor of a mercaptan containing naphtha fraction boiling within the range of about 400 F. which comprises purging said petroleum naphtha with nitrogen to remove any free oxygen which may be contained therein and thereafter contacting said deoxygenated naphtha with tri-normal-buty phosphite employing sufiicient amounts within the range of about 20 to 40 mols of phosphite per mol of mercaptan sulfur and for a time sufiicient to reduce the mercaptan sulfur content of said fraction to produce a doctor sweet product, said contacting being carried out at a temperature within the range of about 50 F. to the initial boiling point of the naphtha treated.

14. A process in accordance with claim 3 in which the alkyl phosphite is triethyl phosphite.

References Cited in the file of this patent UNITED STATES PATENTS 2,413,353 Hunter et a1. Dec. 31, 1946 2,427,173 Withrow Sept. 9, 1947 

1. A PROCESS FOR SUBSTANTIALLY REDUCING THE MERCAPTAN-SULFUR CONTENT AND ODOR OF A MERCAPTAN-CONTAINING PETROLEUM FRACTION WHICH IS SUBSTANTIALLY FREE FROM DISSOLVED OXYGEN, WHICH COMPRISES INTIMATELY CONTACTING SAID FRACTION WITH AN ORGANIC PHOSPHITE FROM THE GROUP CONSISTING OF ALKYL AND CYCLOALKYL PHOSPHITES WHICH IS SOLUBLE IN SAID HYDROCARBON FEED EMPLOYING SUFFICIENT AMOUNTS NOT LESS THAN ABOUT 20 MOLS OF PHOSPHITE PER MOL OF MERCAPTAN-SULFUR AND FOR A TIME SUFFICIENT TO REDUCE THE MERCAPTAN-SULFUR CONTENT OF SAID FRACTION TO PRODUCE A DOCTOR SWEET PRODUCT. 